respiration

• Cellular respiration is an exothermic reaction that transfers energy from glucose and occurs continuously in living cells
• Energy for various reactions in cells is needed and most are catalyzed by enzymes
• There are two types of respiration: aerobic respiration and anaerobic respiration
• Aerobic respiration:

  • Takes place when there is enough oxygen
  • Most efficient way to transfer energy from glucose
  • Takes place continuously in both plants and animals
  • Occurs within mitochondria
  • Word equation: glucose + oxygen → carbon dioxide + water
• Anaerobic respiration:

  • Occurs without oxygen, such as during sprinting
  • Word equation: glucose → lactic acid
  • Inefficient due to incomplete breakdown of glucose molecule
  • Lactic acid buildup needs to be removed later
• oxygen debt is the amount of oxygen required to remove lactic acid
• Nasal passages:

  • Passages leading from the nostrils lined with a moist mucous membrane
• Pharynx:

  • Common passage for the opening to oesophagus and trachea
• Larynx:

  • Voice box containing vocal cords
• Trachea:

  • Breathing tube supported by C-shaped cartilage which prevents the trachea from collapsing as the air pressure in the lungs changes
  • Branches into two bronchi, one to each lung
• Bronchi:

  • Branches repeatedly within the lungs to produce numerous finer tubes called bronchioles
  • The bronchioles at the end of the branching terminate in clusters of air sacs called alveoli
• Cilia:

  • Hair-like structures that cover the epithelial lining of the trachea and bronchi
  • The mucus traps dust, pollen and other particles and the cilia sweeps it upwards into the pharynx
• Alveoli:

  • Sites of gaseous exchange in the lungs
  • Blood entering the lungs from the heart has a lower concentration of oxygen and a higher concentration of carbon dioxide than the atmospheric air entering the alveoli in the lungs
  • Oxygen diffuses from the alveolar air into the blood capillaries
  • Carbon dioxide diffuses from blood capillaries to the alveoli
  • Oxygen and carbon dioxide concentration gradients are maintained by:
  • Continuous flow of blood through the blood capillaries
  • Movement of air in and out of the alveoli, caused by breathing
• Adaptation of Lung for Gaseous Exchange:

  • The numerous alveoli in the lungs provide a large surface area to volume ratio for gaseous exchange
  • The wall of the alveolus is only one cell thick, providing a short diffusion distance for gases
  • A thin film of moisture covers the surface of the alveolus, allowing oxygen to dissolve in it
  • The walls of the alveoli are richly supplied with blood capillaries, maintaining the steep concentration gradient of gases
• Pathway of air during inhalation:

  • Nostrils → Nasal Passages → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
• Nicotine:

  • Addictive substance that stimulates adrenaline release
  • Increases heart rate and blood pressure
  • Increases the risk of blood clot, leading to heart attack or stroke
• Tar:

  • Carcinogenic substances that increase the risk of cancer
  • Paralyses cilia lining air passages, trapping dust and irritants, increasing risks of chronic bronchitis and emphysema
• Carbon Monoxide:

  • Combines irreversibly with haemoglobin to form carboxyhaemoglobin, reducing the efficiency of blood to transport oxygen
  • Increases the rate of fatty deposits on the inner arterial wall, increasing the risk of atherosclerosis
• Irritants:

  • Paralyses cilia lining air passages, trapping dust and irritants, increasing risks of chronic bronchitis and emphysema
• Effect of Smoking on Health:

  • Chronic Bronchitis:
  • Inflammation of respiratory lining of the airways, caused by irritation
  • Excessive mucus secretion due to prolonged exposure to tar and irritant particles
  • Blocked air passages, leading to breathing difficulties and increased risk of lung infections
  • Emphysema:
  • Alveolar walls break down due to persistent and violent coughing
  • Decreased surface area for gaseous exchange, loss of elasticity in lungs, severe breathlessness
  • Lung Cancer:
• • Risk increases due to carcinogens in tobacco, leading to uncontrolled cell division and tumour formation
• Aerobic Respiration:

  • In the presence of oxygen, aerobic respiration produces a large amount of energy
  • Site of aerobic respiration is mitochondria
  • Energy is needed for various cellular processes like synthesising complex molecules, cell growth, muscular contraction, active transport, nerve impulses, and maintaining body temperature
  • Glucose + Oxygen ⟶ Carbon Dioxide + Water + Energy
  • C6H12O6 + 6O2 ⟶ 6CO2 + 6H2O + Energy
• Anaerobic Respiration:

  • In yeast, anaerobic respiration occurs in the absence of oxygen and produces a small amount of energy
  • Does not require mitochondria
  • Glucose ⟶ Ethanol + Carbon Dioxide + Energy (small amount)
  • C6H12O6 ⟶ 2C2H5OH + 2CO2 + Energy (small amount)
• Anaerobic Respiration in Muscles:

  • During strenuous exercise, muscle cells may also respire anaerobically to meet energy demands
  • Buildup of lactic acid in muscle cells leads to fatigue and muscular pains
  • Recovery period involves rest, increased breathing rate to repay oxygen debt, removal of lactic acid from muscles to the liver for conversion back into glucose
• Adaptation of nose:

  • Air passed through nasal passages, is warmed and moistened 
  • Dust, foreign particles and bacteria in the air are trapped by the hairs in the nostrils and mucus on the mucous membrane
  • Harmful chemicals may be detected by small sensory cells in mucous membrane 
• Adaptation of trachea:

  • Gland cells: secrete mucus to trap dust particles and bacteria 
  • Ciliated cells: have hair like structures called cilia on surface, cilia sweep dust trapped mucus up the trachea
• Adaptation of lungs:

  • Numerous alveoli provide large surface area for gas exchange
  • Wall of alveolus is one-cell thick, provides shorter diffusion distance for gases, ensures higher rate of diffusion
  • Thin film of moisture covers inner wall of alveolus, allows oxygen to dissolve in it 
  • Walls of alveoli, richly supplied with blood capillaries, blood flow maintains concentration gradient of gases